The Soft Lens Challenge: A Comparison of
Replacement Schedules

By Robert L Davis, O.D., F.A.A.O., & Edward Williams, O.D.
DECEMBER 1999

This article provides insight on the benefits and differences between two types of soft contact lenses.

Practitioners have good reason to be weary of refitting successful contact lens wearers. Once a patient wears contact lenses without physical awareness, sees clearly and finds the care of the lenses to be simple, there is no reason for them to change modalities. Since the advent of frequent replacement lenses, conventional (reusable lens designs) have faced new challenges and many of them have disappeared due to competition. To this day, however, there are many patients who wear conventional lenses in a variety of designs, and many of these patients wear CSI lenses (Wesley Jessen), against which all conventional lenses are compared. Lens polymers offer idiosyncrasies that cannot be replicated by lens fit alone. It is well known that tear strength, surface binding properties and stiffness or modulus of a material interact to influence the practitioner's lens choice. The Crofilcon A polymer of the CSI lens exhibits excellent optics with impressive deposit resistance and a high modulus of elasticity.

Lens polymers are prone to adsorb proteins found in the tear film of normal healthy eyes. This does not pose a serious problem as long as the lens wearer carries out the prescribed daily cleaning and disinfection process and the lens is replaced prior to surface build-up. However, with inadequate compliance, protein and lipid deposits reduce the clarity of the lens and may cause adverse reactions such as giant papillary conjunctivitis (GPC) or acute red eye syndrome. Noel Brennan, O.D. has calculated that the relative risk of infectious keratitis is about 60 times greater for patients who wear daily wear contact lenses than for nonwearers. The incidence of ulcerative keratitis varies from 41 per 100,000 to 209 per 100,000 for extended lens wearers. The CSI contact lens is different from other HEMA lenses due to the density of the material. The pore size of CSI is 1.9nm, whereas HEMA has a pore size 2.5 to 3.0nm diameters. The CSI material may be less likely to develop deposits and produce an ocular environment that promotes infectious keratitis.

The objective of this evaluation was to challenge the performance of the CSI conventional lens with the performance of the Preference quarterly replacement lens (CooperVision) subjectively by patients and objectively by practitioners. The lens polymer controls handling characteristics, durability and deposit resistance. Comfort, clarity and dryness are qualities that can be designed into a lens. The real question is: can a quarterly replacement lens program offer the same subjective advantage as a conventional lens? Academically, soft hydrophilic lenses don't last forever. Frequent replacement lenses offer an extra level of protection as long as the subjective advantages of conventional lenses can be duplicated.

Materials and Methods

Eighteen healthy subjects with eyes free from ocular pathology were enrolled into the clinical comparison study. Two investigators evaluated 11 female and seven male patients between the ages of 18 and 59. Only long-time asymptomatic daily wear CSI lens wearers were recruited into the study. Practitioners were provided with a pair of CSI lenses (control) and a pair of Preference contact lenses (test) for each patient. The study required patients to report for three office visits (dispensing, 1-week follow-up and 1-month follow-up). In order for the dispensing visit and the fitting visit to occur at the same time, patients' lens prescriptions were pre-ordered. During the dispensing visit, each patient was tested with both the CSI and Preference lens for a direct comparison evaluation. Each patient evaluated the test (Preference) lens on one eye and the control (CSI) lens on the contralateral eye. The practitioners and patients were asked to fill out an evaluation form. The lenses were again placed on the eyes, this time switched, and an additional assessment was documented. After the second evaluation, the test lenses were applied to each eye and dispensed. The test lens was compared to the patients' prior CSI contact lens experience, which acted as the control, or baseline lens in the study.

Each patient was asked to compare the two lenses for comfort, vision, dryness and handling. Patients used the same lens care system that they had been using prior to entry into the clinical comparison study. At the conclusion of the study, each patient was asked if they preferred the test lens or the control lens. Practitioners were asked to compare the two lenses for fit and deposit resistance.

Results

Data were collected at each office visit and tabulated to identify any trends. Although the number of patients enrolled in the study was not large enough to make any statistical analysis or absolute conclusions, the analysis of this study will provide tendency that will give direction for future studies with a sufficient patient population.

Vision -- Of the 18 patients, six (33%) reported superior vision with the Preference lens, four (22%) reported superior vision with the CSI lens, and eight (44%) reported that their vision was the same with both lenses. Vision with the Preference lens was either preferred or ranked equal to the CSI lens 77 percent of the time.

Comfort -- Nine patients (50%) reported that the comfort was equal for both the control and the test lens, while five patients (27%) preferred the comfort of the Preference lens and four patients (22%) preferred the comfort of the CSI lens. Of the total patient population, the Preference lens ranked equal to or better in comfort than the CSI lens 77 percent of the time.

Dryness-- The results of dryness between the Preference and CSI lenses were reported to be equal by four patients (22%). Eight (44%) preferred the Preference lens with respect to dryness, while six (33%) reported the CSI lens to be superior with respect to dryness. Thus, 66 percent of the patients reported the Preference lens as being equal to or better than the CSI lens in this category.

Handling -- The handling characteristics between the two contact lenses were determined by four patients (22%) to be equal. Two patients (11%) preferred the Preference lens with regard to handling, while 12 patients (66%) felt that the CSI lens was superior in this category. Of the total patient population, the Preference contact lens was ranked equal to or better than the CSI contact lens 33 percent of the time.

Fit and Deposit Resistance -- The practitioners involved in this study found no significant difference between the two soft lenses in the categories of fit and deposit resistance.

Conclusion and Related Findings

Seven patients chose the Preference lens and seven patients chose the CSI lens as their preferred lens of choice. Four patients had no clear opinion on their lens of choice. Vision, comfort and dryness performed slightly superior with the Preference lens, while handling was superior with the CSI lens.

In this study, the Preference lens performed in arenas that have traditionally been dominated by the CSI lens, particularly in the area of vision. The Preference lens was also slightly superior to the CSI lens in the categories of comfort and dryness. We selected low-minus powers to challenge the Preference lens further in terms of handling. Patients found the CSI lens to be easier to handle, although they were impressed enough with the Preference lens in other respects to rate the two lenses equally overall.

This study did not address the issue of wearing schedules. When fitting contact lenses, practitioners must decide upon wearing schedules since conventional and frequent replacement lenses offer different advantages. Conventional lenses have a long history of success with replacing a lens when a problem relates to deposits, fractures or aged surfaces. We have learned from conventional lenses that practitioners must become proactive with the frequent replacement of lenses. Now we replace lenses before problems develop. The fitting paradigm shift has not eliminated adverse reactions, although it has significantly reduced some of the problems related to torn lenses and deposit-laden lenses. The materials and designs of frequent replacement lenses are not necessarily superior to those of conventional lenses, but due to their equivalency and their replacement schedule, practitioners feel that they provide an extra level of protection.

Although the incidence of acute red eye (ARE) and giant papillary conjunctivitis (GPC) had a lower incidence rate when lenses were replaced at least every three months, in Grant's investigation of the incidence of ARE and GPC related to the frequency of lens replacement, he found that the incidence of microbial keratitis was unchanged by the frequency of lens replacement.

Gundel and Rosen evaluated the value of two-week and three-month lens replacement as perceived by patients with regard to comfort and vision. The study's results demonstrated that practitioners should determine the appropriate frequency of lens replacement by safety, efficacy and cost factors. There is no difference subjectively in comfort and vision between the two wearing schedules.

This pilot evaluation compared the CSI conventional contact lens to the Preference quarterly replacement contact lens with subjects who had been habitually been wearing CSI lenses. Vision, comfort and dryness proved to be equal between the two lens modalities, but handling was superior with the CSI lens. Even with the advances made in lens care solution regimens, the surface quality of a six-month old CSI lens cannot compete with a new Preference quarterly replacement lens.

A frequent replacement contact lens helps protect the eye from adverse reactions in patients who have poor lens hygiene and who over wear their lenses. Regular replacement creates a deposit-free surface with good wettability properties. Taking a preventive approach and replacing a lens prior to a reduction in visual acuity or comfort or positive biomicroscopy findings will avoid many soft lens wear complications. This study demonstrates that the Preference quarterly replacement lens is equivalent to the CSI lens, but offers the advantage of preventative lens replacement. CLS

References are available upon request to the editors at Contact Lens Spectrum. To receive references via fax, call (800) 239-4684 and request document #55. (Be sure to have a fax number ready.)

Dr. Davis is currently developing an eyecare specialists practice outside chicago. He is presently chair of the Contact Lens Section of the American Optometric Association.

Dr. Williams is in private practice in Denver, Col., specializing in contact lenses. He is also a member of the American Academy of Optometry.